Method of operating an internal combustion engine

ABSTRACT

A method is proposed for operating an internal combustion engine provided with gas exchange valves in which the gas exchange valves are maintained in their open and closed positions by the holding force of magnets. When internal pressure within a cylinder increases sharply during the combustion process the holding force for maintaining the valve in its closed position is reduced.

The invention relates to a method of operating an internal combustionengine as defined in the generic portion of claim 1.

An internal combustion engine of this kind is known, for instance, fromDE-OS No. 30 24 109. The gas exchange valve or valves are maintained intheir closed position in that an electromagnet is energized and attractsan armature. A spring system biases the valve in the opening direction,so that upon deenergization of the electromagnet the spring systembecomes active and opens the valve. However, when the electromagnet isenergized its force is sufficient to maintain the armature in the closedposition the bias of the spring system notwithstanding.

Hence, it is necessary to use electrical energy to maintain the valve inits closed position.

The task of the invention resides in operating an internal combustionengine equipped with a gas exchange valve in such a manner that theenergy requirements are reduced. As used herein, the term gas exchangevalve is intended to connote either fuel intake valve or exhaust valve.

The task is solved by the elements enumerated in the main claim.

In accordance with the invention use is made of the fact that during thecombustion process high internal pressure develops in the interior of acylinder which high pressure is acting upon the valve head. Thus thevalve is subjected to a force which additionally pushed it against itsseat in the direction of closing. During the effectiveness of this forcethe holding force to be generated by the magnet may therefore be reducedfor the magnet need now only compensate for the spring bias less theforce acting upon the valve head.

Since the internal pressure of a cylinder is not constant during thecombustion process, the flow of current through the electromagnet, in apreferred embodiment of the invention, is controlled, the degree ofcurrent flow being dependent from the interior pressure of the cylinder.

It is difficult to derive a direct measure of the interior pressure ofthe cylinder; however empirical values indicative of the buildup of theinterior pressure are available. Therefore, in accordance with apreferred embodiment of the invention the flow of current through theelectromagnet may be controlled as a function of time whereby the levelof current flow is a function of the empirically determined buildup ofinterior pressure within the cylinder during a combustion or compressionphase.

When the interior pressure in the cylinder exceeds the force of thespring for pushing the valve into its open position the flow of currentthrough the magnet may even be completely discontinued.

For synchronizing the pattern of current flowing through theelectromagnet with the build-up of pressure in the cylinder, the instantof ignition may be utilized, for because of the ignition of the mixturewithin the cylinder the interior pressure rises sharply beginning withthe instant of ignition. Thus, the instant of ignition defines thestarting point for the buildup of the interior pressure in the cylinder.

The invention is explained hereinafter on the basis of the drawing.

FIG. 1 is a schematic presentation, in longitudinal section, ofstructure for practicing the invention; and

FIG. 2 is a diagram of the operation of a four cycle piston engine forexplaining the invention.

As mentioned supra, the method in accordance with the invention may bepractised in an internal combustion engine of the kind disclosed byDE-OS No. 30 24 109. It is essential that the valve arrangement be asfollows: A cylinder head 10 encloses the upper portion of the internalchamber 12 of a cylinder within which combustion processes of the kindcustomary in a combustion engine take place in a known manner. A valve14, shown in FIG. 1 in its open position, i.e. lifted from its seat, isprovided for opening the intake and/or the exhaust. At its shank 16 thevalve 14 is provided with an armature plate 18 which may axiallyoscillate to and fro between pole faces of a magnet 20 and a magnet 22.When the armature plate 18 is attracted against the magnet 20 the valveis open, and when the armature plate 18 is attracted against the magnet22 the valve 14 is closed. However, the valve 14 is not moved from itsengagement with the pole face of a magnet into engagement with the poleface of the other magnet by magnetic attraction forces; rather, there isprovided a system of springs 24, 25, 26, 27, the springs 24 and 25pushing the armature plate 18 from its engagement with the pole face ofthe magnet 22, whereas the springs 26 and 27 push the armature plate 18out of engagement with the pole faces of the magnet 20. The null of thisspring system is such that when the magnets 20 and 22 are not energizedthe armature plate 18 assumes a position substantially halfway betweenthe pole surfaces of the magnets 20 and 22.

As shown in FIG. 1 the magnet 20 is energized to maintain the armatureplate 18 in engagement with the pole face of the magnet 20 even thoughthe armature plate 18 is subjected to the force of the springs 26 and 27which bias the armature plate 18 in a direction away from the pole face.When current flow through the magnet 20 is discontinued the armatureplate 18 is accelerated by the springs 26 and 27 which acceleration isretarded upon engagement with the springs 24 and 25 but which issufficient to move the armature plate 18 at least adjacent the pole faceof the magnet 22. If at this instant the magnet 22 is energized thearmature plate 18 will be maintained in engagement with the pole facesof the magnet 22 and the valve 14 is closed.

To maintain the valve 14 in its closed position it is necessary tomaintain current flow in the electromagnet 22.

The level of current must be such that it compensates for the force ofthe springs 24 and 25.

In accordance with the invention it has been recognized that during aportion of an operating cycle of a four cycle combustion engine, or of atwo cycle engine provided with valves, an additional force is applied tothe head of the valve 14 which force presses the valve against its seat.This force acts in the same direction as the force to be generated bythe electromagnet 22 for attracting the the armature plate 18 so thatthe force to be applied by the electromagnet 22 may be reduced by theforce generated by the internal pressure in the cylinder.

FIG. 2 depicts a diagram of an operational cycle of a four cycleinternal combustion engine; as is known, an ignitable mixture is drawninto the cylinder chamber during phase I; during phase II, positionedbetween 180° and 360° of rotational crank shaft angle, i.e. between theupper and lower dead center positions, the mixture is compressed forignition shortly before the upper dead center has been reached.Therefore, after the upper dead center has been reached the internalpressure in the cylinder increases sharply during phase III, and asubstantial pressure is exerted against the head of the piston fordriving the internal combustion engine. In conventional four cycle Ottoengines the pressure may go as high as 40 bar; in Diesel engines it maybe noticeably--about three times--higher.

During phase IV the burnt up mixture is exhausted.

Especially during phase III, the working cycle, very high pressures aregenerated within the cylinder which push the valve 14 against its seat.During this interval, i.e. between substantially 380° and 480° duringthe course of the 720° rotational crank shaft angle, the flow of currentthrough the magnet 22 may be reduced without any danger of the springs24 and 25 pushing the valve 14 into its open position.

Advantageously, the flow of current is not controlled as a function ofthe absolute value of the rotational crank shaft angle; rather the flowof current should be synchronized with the instant of ignition. Thereduction in current flow through the electromagnet 22 may commence at apredetermined point in time following the instant of ignition, that isto say at a predetermined rotational angle of the crank shaft since itis independent of the rotational speed, and may be maintained, dependingupon the characteristics of the engine, for about 100° of crank shaftangle. During this 100° interval the flow pattern of the current may becontrolled, or it may simply be reduced to a lower level.

I claim:
 1. A method of operating an internal combustion engine havingat least one gas exchange valve actuated by an electromagnet for closinga combustion cylinder during an operating cycle of said engine,comprising the steps of:energizing said electromagnet with current of alevel sufficient to move said valve into a position closing saidcylinder; building up pressure within said cylinder; and reducing saidcurrent level in said electromagnet in response to said pressure.
 2. Themethod of claim 1, wherein reducing said current level is controlled asa function of time related to the buildup of pressure within saidcylinder.
 3. The method of claim 2, wherein said valve is moved to itsclosing position against the bias of a spring, and wherein the step ofreducing said current level is taken when said pressure within saidcylinder has built up to a level acting upon said valve with a force inexcess of the bias of said spring.
 4. The method of claim 3, whereinignition takes place within said cylinder and said step of reducing saidlevel of current is substantially synchronized with said ignition. 5.The method of claim 3, wherein the flow of current is discontinued whenthe increased pressure within the cylinder exceeds the bias of thespring.
 6. The method of claim 4, wherein said engine is a four cycleengine having a 720° duty cycle and said ignition occurs at about 345°and wherein said level of current is reduced in the range from about380° to about 480°.